Philadelphia Zoo tigers are now able to move beyond their usual enclosures thanks to a recently unveiled series of fenced-in passageways that allow the massive felines to roam into new areas via an archway over the zoo's main promenade as zoo patrons watch from below.

The project, known as the Big Cat Crossing, cost $2.3 million to construct and is the latest addition to the zoo's travel system, which has a similar trail for small primates and another for orangutans, The Associated Press reported.

The concept behind the overhead enclosure, known as animal rotation, is to increase the animal's stimuli at the zoo by giving them the opportunity to travel beyond their usual habitats and encounter different sites like they would in the wild.

According to American Association of Zoo Keepers CEO Ed Hansen, animal rotations at zoos have become increasingly popular as "the public challenges zoos to improve."

"It's to replicate the natural environment as best as we can," Hansen told the AP. "It's enriching to their environment and their mental capacity."

At Washington's National Zoo, the O Line similarly allows orangutans to travel between enclosures by swinging through a system of cables contained within overhead enclosures. At the Denver Zoo, African wild dogs, hyenas, and lions are frequently rotated between habitats to change their stimuli.

In addition to tigers, the Big Cat Crossing will eventually be opened up to lions and snow leopards as well. Over time it will be expanded from its current length of 330 feet.

Philadelphia Zoo tigers are now able to move beyond their usual enclosures thanks to a recently unveiled series of fenced-in passage ways that allow the massive felines to roam into new areas via an archway over the zoo's main promenade as zoo patrons watch from below.